1. Field of the Invention
The present invention relates to powder-coating compositions, specifically to powder-coating compositions containing additives that improve the transfer efficiency of the powder-coating compositions.
2. Description of the Related Art
It is known that during the application of a powder-coating composition on to substrate, not all of the coating composition ends up on the substrate. The amount of powder-coating material being applied on to a substrate that actually ends up on the substrate as the powder coating relates to the transfer efficiency of the process. The transfer efficiency can be calculated by dividing the change in weight of the substrate by the change in weight of powder coating source dispensing the powder coating composition wherein the change in weight is the weight difference before and after the application of the powder coating. The transfer efficiency is conveniently expressed as a percent.
Although the powder coatings market is growing rapidly, one of the limiting factors for continued growth is the transfer efficiency. Typical powder coating application lines have powder transfer efficiency from spray point to substrate of about 70% or greater. The remaining powder has to be reclaimed and re-sprayed. Although this respray ability enables the powder coatings industry to cite lower coating costs than liquid, solvent-based coatings it does decrease the efficiency of the process. Furthermore, in some applications recycling powder is not possible because of quality control reasons. One such area is in automotive clear coat applications. In these applications, the recycled material may contain lint or other foreign matter that is likely to cause defects in the finished coated automotive part.
Also, when using metallic or other dry blended systems (expensive color, etc.), the components may not transfer at equal rates (for example, metallic pigments or colors transfer at a different rate than the rest of the coating). Any reclaimed material looks different than the originally transferred coating. Thus spraying reclaimed material here amounts essentially to spraying to waste. This adds further cost to an already expensive dry blending process that is used to mix some of the components together to make the coating. Clearly there is a need for improving the transfer efficiency of powder coatings. The present invention fulfils such a need.
A transfer efficiency additive can positively affect the economics of the powder coating process. If recycling and reclaiming of powder-coating compositions are not feasible or desired, as mentioned above for automotive clear coats or when using metallic colors, then an efficient first-pass transfer becomes even more important. Two other factors that could be affected by a transfer efficiency additive are: 1) an improvement in the ability of the powder spray to penetrate into corners and close spaces, and 2) improving the ability of very small size powder coating particles to efficiently transfer and build on a metal substrate. Some industry sources estimate that an increase of about 3 to 5% in transfer efficiency would justify the cost involved in adding a transfer efficiency additive to achieve this increased transfer efficiency.
U.S. Pat. No. 5,780,401, Steckel, Jul. 14, 1998, discloses coating additives useful as non-flatting slip-enhancing agents that are non crosslinked reaction products of
(a) an amine represented by the formula NR1R2H wherein each R is independently selected from the group consisting of hydrocarbyl groups and hydroxyalkyl groups; or by the formula Dxe2x80x94(NGH)y wherein D is a multivalent organic radical having 2 to about 30 carbon atoms; each G independently is hydrogen, a hydrocarbyl group, or hydroxyalkyl group; and y is at least 2; provided that if D is an organic radical containing 2 carbon atoms and y is 2, at least one G must be a hydrocarbyl group of 1 to 30 carbon atoms; and
(b) a carboxylic acid of the formula Bxe2x80x94(COOH)z, or a reactive equivalent thereof, wherein B is a direct link between two COOH groups, a mono- or a multivalent organic radical, and z is 1-5; wherein the resulting product contains at least 2 hydrocarbyl groups each having about 12 to about 30 carbon atoms.
Japanese Laid-Open Patent Publication No. 5-112749, Nakatsuka et al., May 7, 1996, discloses a powdered polyethylene resin composition for powder paints, consisting of (A) 100 parts by weight of a resin mixture of ethylene-vinyl acetate copolymer and polyethylene, the content of said ethylene-vinyl acetate copolymer being 1 to 40% by weight, and (B) 0.02 to 0.5 part by weight of a fatty acid amide. When used in coating, the resulting coating film was disclosed to have good slip property with less reduction of the surface gloss.
Japanese Patent Publication No. 61-21977, Tada, May 16, 1984 discloses a powdered smoothing agent for powder paints prepared by heating and fusing at 210xc2x0 C. or less a mixture of an amide wax obtained by the reaction of a carboxylic acid and an amine and having a melting point of 50xc2x0 to 145xc2x0 C. and an acrylic polymer having an average molecular weight of 1000-10000 and a glass transition temperature of 20xc2x0 C. or less at a weight ration of the former to the latter ranging from 60:40 to 90:10; and cooling and powdering the cofused product, wherein said acrylic polymer is a homopolymer or copolymer, and said homopolymer or copolymer comprises as monomer components 70% or more of an alkyl(meth)acrylate having an alkyl component of 2-18 carbon atoms and optionally 30% by weight or less of a monomer copolymerizable with said (meth)acrylate monomer.
This invention relates to a powder coating composition made by combining at least two components comprising:
A) a film forming thermosetting resin composition, and
B) a transfer-efficiency enhancing amount of at least one amide; wherein component (B) is incorporated into the powder coating composition by the addition of component (B) to an extruded composition comprising components other than (B).